This invention relates to an apparatus and method for the use of a high velocity and temperature injection lance to enhance the performance of industrial furnaces. This injection lance advantageously combines the traditional functions of burners and gas, liquid, or solid reagent injectors. Burners produce flames that are used as heating sources for high temperature industrial processes such as the melting of glass or metals. Injectors advantageously add gaseous, liquid, or solid reagents to industrial processes for such purposes as the decarburization of stainless steel, for example. The injection lance of this invention uses linear or curvilinear flame nozzles to produce high velocity and high temperature flame jet sheets with a well defined geometry to more efficiently provide heat and/or reagents to industrial furnaces.
The term flame nozzle is commonly used to describe hand-held torches that produce high velocity, high temperature, and well-defined flame jets that are used in metal fabrication and spray deposition coating. These jets are often supersonic. A flame nozzle, at least partially, mixes oxidant and fuel, initiates combustion within a cavity, and then accelerates the burning gases through a nozzle to produce a well defined high velocity flame jet.
A burner either feeds fuel and oxidant separately (a tip mixed burner) or feeds a fuel and oxidant mixture (a premixed burner) to a flame ignition source in order to produce a flame envelope. The velocity of these gases must be less than the flame velocity in order for the flame to be able to propagate along the flame jet axis from a downstream ignition source. When the gas velocity is greater than the flame velocity, then the flame envelope `lifts off` the burner tip and is reestablished when the velocity of the combustion gases decreases to velocity that is equal to or less than the flame velocity.
If excessive combustion occurs before the hot gases pass through a flame nozzle, the nozzle body may overheat. U.S. Pat. No. 4,067,686 patent sets forth a method to produce a core of very hot burning gases located within a layer of high velocity gas in order to protect the conical flame nozzle. U.S. Pat. No. 4,653,692 describes a torch nozzle in which the fuel is introduced upstream of the oxidant which then mixes in a turbulent zone and homogenizes in a homogenizing zone inside the conical nozzle. U.S. Pat. No. 5,343,693 describes an approach to change the relative position of the premixed injection slot and conical flame nozzle in such a manner that the flow speed of the premixed gas can be maintained substantially constant even if the premixed gas flow rate is changed and, accordingly, prevent backfire or blow out of a flame. There is, however, a problem scaling-up these conical nozzles. The flow rate of gas leaving a nozzle increases roughly with the square of the nozzle diameter and the area for flame initiation, represented by a surface parallel to the cone, is roughly proportional to the nozzle diameter. It becomes, therefore, progressively more difficult to initiate combustion in the region of the flame nozzle with increasing flame nozzle diameter and throughput.
In the case of the conical flame nozzles, e.g. U.S. Pat. Nos. 4,067,686, 4,653,692, the gas fuel passage, gas oxidant passage, and flame nozzle are roughly coaxial, the flame is propagated in a zone between the fuel nozzle and the flame nozzle along a conical path that is roughly collinear with the gaseous fuel and gaseous oxidant flow path with a progressively decreasing cross sectional area. As a result, there is an optimum fuel nozzle to flame nozzle distance that is a complicated function of the flame nozzle diameter, fuel and oxidant feed velocities, flame velocity, and stoichiometry.
For larger scale flame nozzles, the prior art teaches use of super stoichiometric combustion rather than short residence time to control the nozzle temperature. For example, U.S. Pat. No. 5,266,024 teaches production of a high velocity and high temperature oxygen jet by mixing greater than 80% excess oxygen (CH.sub.4 +(2+.alpha.)O.sub.2.fwdarw.CO.sub.2 +2H.sub.2 O+.alpha.O.sub.2, where.alpha.&gt;1.6) and fuel in a stage wise manner in a stage wise manner in a mixing chamber and allowing the hot oxygen combustion gases stream to exit the chamber at a velocity greater than 200 feet per second. U.S. Pat. No. 5,533,331 teaches a similar approach for missile divert thrusters and attitude control thrusters. U.S. Pat. No. 4,549,866 teaches the addition of excess oxidant to the nozzle combustion chamber and discharge of this excess oxygen from separate nozzles in a cone from the flame nozzle. However, these strategies do not allow the production of large, high temperature, and high velocity flame jets that could be useful in industrial furnaces.
Rocket engines comprise the most common example of large scale flame nozzles. Rocket engines typically overcome the drawbacks of the aforementioned prior art by using plurality of fuel and oxidant inlets, e.g. U.S. Pat. Nos. 5,438,834, 5,557,928, 5,704,551 to solve the scaling problem and by using very complex nozzle cooling systems, e.g. U.S. Pat. Nos. 4,109,460, 5,557,928, 5,619,851, 5,683,033, and 5,832,719 to provide the required cooling. These techniques, however, have not proven to be appropriate for industrial process due their inherent high cost and long term reliability problems.
Flame jet nozzles have found use for the production of thermal spray coatings. Very high rate of heat and momentum transfer are required to produce high quality coatings. U.S. Pat. Nos. 4,562,961, 4,678,120, 4,836,447, 4,999,225 teach various approaches to have particles entrained into high velocity flame jets from cylindrical flame nozzles by contacting the particles with the exterior of the cylindrical flame jet. These particles could be heated and accelerated much more rapidly if the particles could be fed to the center of the flame jet. However, with conical flame jet nozzles, the particles would certainly cause nozzle erosion problems. U.S. Pat. No. 5,384,164 uses a supersonic flame jet to melt a metallic wire feed and accelerate the molten metal.
Conventional oxygen cutting nozzles use high velocity oxygen jets in conjunction with a pre-mixed or tip mixed flame to cut steel plate. U.S. Pat. No. 4,344,606 teaches an approach to increase the cutting efficiency by having the oxygen jet intersect with the flame jet prior to contacting the steel plate.
In co-pending U.S. patent application Ser. No. 09/053,112 a particulate injection burner is disclosed which uses separate gaseous fuel and gaseous oxidant outlets to produce a mixture of gaseous fuel and gaseous oxidant in a chamber upstream of a converging and diverging flame nozzle. The mixture of fuel and oxygen is accelerated through a converging and diverging nozzle prior to combustion.
The prior art flame nozzles have not provided a burner for larger scale industrial applications which offers the scaled-up size necessary for industrial furnaces without encountering problems of overheating without resorting to complex, costly or constrained designs. Nor does the prior art teach a practical approach to produce multiple coaxial flame jets. Finally, the prior art does not disclose a burner in which the reagents are not required to flow through flame envelopes or flame jets.